# led question

Discussion in 'Electronic Basics' started by Klemen, Jul 1, 2003.

1. ### KlemenGuest

Hi!

I'd like to connect 5 leds, but i'm not sure which way is better. Is it ok
to connect them in series with a restitor to limit the current, or should i
connect them parallel each with the resistor?

regards
Klemen

2. ### John PopelishGuest

Either of those may work, but connecting several in series may make
more efficient use of the supply voltage, if it is quite a bit higher
than the LED requirements. What supply voltage are you using, and
what color of LED?

3. ### KlemenGuest

I'm using 12V(actually 14V because it's a car battery) power suply and
bright blue leds.

4. ### John PopelishGuest

Since getting the utmost efficiency is not so important (unless you
are going to leave them on for days without running the car) I would
connect them in series in pairs , with a resistor for each pair.
Since car battery voltage can spike around and vary quite a bit, I
would go for about 10 ma (.01 amp) average. Blue LEDs drop about 3.5
volts, each, so a pair will use up about 7 volts. That leaves about 7
volts to be dropped by each resistor while carrying about .01 amp.
7/.01=700 ohms, which is not a standard 5% value. 680 or 750 ohms
would work fine. The heat produced in each resistor is about
..01*.01*700=.07 watts, so 1/4 watt resistors are plenty big.

Hi!

The way you connect 5 leds doesn't make a difference in terms of theory.
You can build parrarel or series cicuit. Either way is good because in both
connections current flowing through leds must be the same and the voltages
dropped on them also. So, the only difference betwen both types of
connection
is the voltage applied and the number of resistors. You should decide which
is better: use more resistors and less voltage or vice versa.

6. ### KlemenGuest

Thank you everyone for your help!

regards
Klemen

7. ### romaGuest

So when one goes bad they all go out .
roma

8. ### John PopelishGuest

If it goes bad by going open circuit, then that string will go out.
If it goes bad by going short circuit, the rest of the string gets
brighter. If the LEDs are operated well within their ratings (say
half of maximum current rating) either case is very unlikely in your